add nasm-segelf build recipe [#146]

... for homebrew package manager.

makefile

@@ -10,6 +10,7 @@ define mdir
 endef
 
 all:
+	$(MAKE) nasm-segelf
 	+$(call mdir,fdpp,all)
 
 clean:
@@ -21,3 +22,7 @@ rpm: fdpp.spec.rpkg
 
 install uninstall deb tar:
 	cd fdpp && $(MAKE) srcdir=$(srcdir)/fdpp $@
+
+nasm-segelf:
+	$@ --version 2>/dev/null || \
+		brew install $(srcdir)/nasm-segelf.rb

nasm-segelf.rb

@@ -0,0 +1,34 @@
+class NasmSegelf < Formula
+  desc "nasm-segelf"
+  homepage "https://github.com/stsp/nasm"
+  url "https://github.com/stsp/nasm.git", branch: "elf16"
+  version "2.17"
+  sha256 ""
+  license "BSD-2-Clause"
+
+  depends_on "autoconf" => :build
+  depends_on "automake" => :build
+  depends_on "gcc" => :build
+  depends_on "perl" => :build
+  depends_on "make" => :build
+
+  def install
+    system "./autogen.sh"
+    system "./configure", "--prefix=#{prefix}"
+    system "make", "install"
+  end
+
+  test do
+    (testpath/"foo.s").write <<~EOS
+      mov eax, 0
+      mov ebx, 0
+      int 0x80
+    EOS
+
+    system "#{bin}/nasm-segelf", "foo.s"
+    code = File.open("foo", "rb") { |f| f.read.unpack("C*") }
+    expected = [0x66, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x66, 0xbb,
+                0x00, 0x00, 0x00, 0x00, 0xcd, 0x80]
+    assert_equal expected, code
+  end
+end